Using the classically conditioned rabbit nictitating membrane response as a model system for studying mammalian learning and memory, support is sought for anatomical investigations of the neuronal control of this behavior. The specific aims are to map the accessory abducens nucleus of the brain stem in terms of the distribution of motoneurons and course of axonal projections to the principal extraocular muscles involved in the NMR. This will be accomplished by two methods of peripheral application of horseradish peroxidase (HRP). The other principal objective is to contrast the sites of origin within the brain of afferent projections to the abducens and accessory abducens nuclei by central application of HRP. Such information is essential for understanding the neuronal basis of the conditioned response.